@R: red;

html,
body {
    height: 100%;
    overflow: hidden;
    background: lightblue;
}

#app {
    font-size: 20px;

    a {
        color: @R;
        transition: color .3s;

        &:hover {
            color: darken(@R, 20%);
        }
    }
    .box1{
        width: 200px;
        height: 200px;
        background: url('./images/girl.jpg') no-repeat;
        background-size: 100% 100%;
    }
}